A Hybrid Automatic Repeat reQuest (HARQ) is adopted in a long term evolution system to improve the reliability of data transmission, and when the downlink HARQ function is enabled, a user equipment decodes a received downlink data packet and feeds back acknowledgement (ACK) to a base station if it is decoded correctly or feeds back non-acknowledgement (NACK) and requests the base station to retransmit the data packet if it fails to be decoded. At the end of a downlink persistent scheduling service, the base station transmits a Semi-Persistent Scheduling (SPS) resource release instruction to the user equipment to instruct the user equipment to release all the resources allocated to the service, and the user equipment feeds back ACK to the base station upon correct reception of the instruction. The user equipment will use an uplink control channel resource to transmit the ACK/NACK feedback information to the base station over the uplink control channel to thereby perform an HARQ process.
In a general transmission solution of the long term evolution system (Rel-8) which has been substantially established in the ongoing standardization effort, schematic diagrams of multi-carrier bandwidth allocation of a Frequency Division Duplexing (FDD) system and a Time Division Duplexing (TDD) system are as illustrated respectively in FIG. 1 and FIG. 2, where a downlink control signaling zone, a downlink data zone, an uplink control signaling zone and an uplink data zone and their transmission relationships with each other are defined respectively for each operating carrier. Particularly, uplink control signaling occupies both ends of a frequency band and is transmitted in a frequency-hopping mode, that is, the uplink control signaling will be transmitted over different frequency bands in two timeslots of a sub-frame.
For a dynamically scheduled downlink data packet, the index of an uplink control channel resource for its ACK/NACK feedback information will be derived from the index of a Control Channel Element (CCE) occupied by a Physical Downlink Control Channel (PDCCH) over which scheduling information of the data packet is borne, that is, a unique uplink channel resource index can be derived from a CCE index. In the LTE Rel-8 system, the user equipment transmits only one uplink control channel at most in each sub-frame due to the limit of single-carrier transmission in the uplink so that the actually used uplink control channel is an uplink control channel corresponding to a first CCE occupied by the downlink control channel of the user equipment.
In the ongoing study of an uplink control channel in the long term evolution system, it has been proposed to use Orthogonal Resource Transmit Diversity (ORTD) for transmit diversity in uplink control channel transmission performed by a user equipment configured with two or more transmission antenna ports, i.e., a user equipment with multiple transmission antenna ports, to thereby improve the reliability or capacity of transmitting uplink control signaling. The so-called ORTD refers to that each antenna port corresponds to an uplink control channel resource and the same information is transmitted via respective antenna ports after being spread by orthogonal sequences selected from resource indexes of the different antenna ports. A receiver picks out and then performs combined detection on signals from the different antenna ports to thereby achieve a diversity gain. FIG. 3 is a schematic principle diagram of transmit diversity in ORTD with two antenna ports, where s is fed-back ACK/NACK information, and n1PUCCH and n2PUCCH represent the indexes of two different uplink control channel resources over the two antenna ports respectively. The UE will feed back ACK/NACK information over the two feedback channels for transmit diversity of a PUCCH.
In the LTE Rel-8 system, for a user equipment, a Physical Downlink Control Channel (PDCCH) over which a Physical Downlink Shared Channel (PDSCH) corresponding to the user equipment is scheduled and also possibly a PDCCH over which a Physical Uplink Shared Channel (PUSCH) corresponding to the user equipment is scheduled exist in a downlink sub-frame to be fed back. The index of an uplink channel available when the user equipment feeds back ACK/NACK is determined from the index of a first CCE of a PDCCH over which a PDSCH of the user equipment is scheduled or an SPS resource is instructed to be released, and not all the CCEs of the PDCCH over which the PDSCH of the user equipment is scheduled have been used.
In a Long Term Evolution-Advanced (LTE-A) system, if transmit diversity of a Physical Uplink Control Channel (PUCCH) is to be supported for a user equipment configured with multiple transmission antenna ports, each of the antenna ports has to be configured with an uplink control channel resource, so it is required to limit the number of CCEs in a control zone, in a downlink sub-frame to be fed back, corresponding to the user equipment or to limit the aggregation level of CCEs of the PDCCH or to limit both of them, and this will influence the flexibility of PDCCH scheduling and the complexity of blind detection of the user equipment on the PDCCH.